Many efforts are underway to replace the magnetizable coatings conventionally used in magnetic recording media, which comprise magnetizable particles dispersed in organic binder, with metallic thin-film magnetic layers. The latter layers are considered to be capable of a higher density of information storage, especially when they have an easy axis of magnetization perpendicular to the surface of the layer (see U.S. Pat. No. 4,210,946), which makes possible perpendicular recording.
A major problem with metallic thin-film magnetic recording media is their susceptibility to wear. Record/playback transducer heads contacting the metallic thin film will have a tendency to erode or otherwise damage the film. Even slight erosion will result in considerable loss of data when high bit density recording is employed. Applications which would involve erosion and severe wear of metallic thin film magnetic media are on the increase, with video tape and electronic cameras being two examples.
One approach to increase the life of metallic thin film media is to apply some sort of protective covering over the layer, such as a fluorinated polyether (see U.S. Pat. Nos. 3,778,308, 4,267,238; and 4,268,556). This covering, known as the lubricant or top coat, functions to lubricate, add corrosion protection, and give wear resistance to the magnetic medium.
The lubricating or top coat layer should be firmly anchored to the magnetic recording layer so that it will not be removed or cause clogging of the recording or playback heads, but in most cases in the prior art, it is believed that fluorinated lubricants have been applied as coatings from halogenated solutions or emulsions with no means, other than physical absorption or adsorption, of bonding the lubricant to the magnetic recording medium. Commonly assigned U.S. Pat. 4,404,247 discloses a protective covering for magnetic recording media comprising: (a) an inner layer of film forming aromatic or heterocyclic polymerizable monomer and vinyl aromatic polymer, and (b) an outer layer of a compound containing perfluoropolyether segments (often referred to herein simply as "perfluoropolyether"). The above materials can be separately applied in solution to magnetic recording media in two coating steps and be subsequently in-situ polymerized. The contiguous monomers of the two layers are said to apparently copolymerize, bonding the perfluoropolyether segments to the magnetizable coating through the inner layer. The perfluoropolyether lubricant is said to have a significantly greater adherence to the metallic thin-film magnetizable layer on the recording medium than it would have if it had been directly applied, because of the inner layer material. Since the monomers of the inner layer are soluble in organic solvents and the perfluoropolyether is soluble in fluorinated solvents, two separate coating steps were used.
It is the object of this invention to avoid the need for two separate coating steps by providing a single coatable mixture of a perfluoropolyether and a solubilizing agent, which mixture is soluble in a common non-fluorinated solvent. It is a further object to use as the solubilizing agent a material that functions as a primer material, i.e., increases the adhesion or anchoring of the perfluoropolyether to a metallic substrate, and particularly to a thin-film metal substrate of a magnetic recording medium.